1. Field of the Invention
The present invention relates to a high-frequency semiconductor device, particularly to the patch antenna provided in an MMIC (Monolithic Microwave Integrated Circuit).
2. Related Prior Art
MMICs comprising high-speed semiconductor devices such as represented by HEMT (High Electron Mobiliy Transistor) or HBT (Hetero-Bipolar Transistor) are provided with an antenna for receiving and transmitting signals from/to the outside. Antenna called patch antenna is known as what is easy to intergrate with MMICs.
FIG. 1 is a see-through plan view for explaining a conventional patch antenna, and FIG. 2 is a cross-sectional view taken on segment line A-Axe2x80x2 in FIG. 1.
Referring to FIGS. 1 and 2, conventional patch antenna 100 has a structure comprising semiconductor substrate 1 provided with surface insulation film 2 protecting the surface thereof, antenna-ground plane 3 provided thereon, which is to be connected to the ground potential, and patch electrode 6 and antenna line 6a for supplying power to patch electrode 6 (or extracting power from patch electrode 6), both formed on antena-ground plane 3 with interlayer insulation film 5 therebetween.
The conventional patch antenna described with reference to FIGS. 1 and 2 can be formed from a planer metallization pattern, and easily integrated in an MMIC.
Patch electrode 6 corresponds to the feeding portion of the antenna, and its shape plays a substantial role in determining the characteristics of the antenna. However, it is necessary to connect antena line 6a to patch electrode 6, and this results in that the effective patch electrode has a shape of combining the respective patterns of patch electrode 6 and antenna line 6a. Thus, the conventional patch antenna necessarily includes the pattern of antenna line 6a, and the antenna characteristics, for example, radiation pattern, deviate from the ideal values obtained from the design based on only patch antenna 6.
It is an object of the present invention to provide an MMIC having a patch antenna with improved antenna characteristics.
It is another object of the present invention to provide a method for increasing freedom in a patch antenna pattern design.
It is still another object of the present invention to provide a method for preventing patch electrode from the influence of antenna line 6a. 
FIG. 3 is a see-through plan view for explaining the essential concept of the presnt invention, and FIG. 4 is a cross-sectional view taken on segment line A-Axe2x80x2 in FIG. 3.
As shown in the drawings, antenna line 6a as the antenna connection portion is formed under antenna ground plane 3, and is connected to the lower surface of patch electrode 6 via through-hole 7.
According to the present invention, antenna line 6a is not formed on the top surface of interlayer insulation films 5, and the pattern shape of patch electrode 6 can be free from antenna line 6a, and thus, the antenna characteristics can be improved.